Dispersive liquid–liquid microextraction and injection-port derivatization for the determination of free lipophilic compounds in fruit juices by gas chromatography-mass spectrometry

A method consisting of dispersive liquid–liquid microextraction (DLLME) followed by injection-port derivatization and gas chromatography-mass spectrometry (GC–MS) for the analysis of free lipophilic compounds in fruit juices is described. The method allows the analysis of several classes of lipophilic compounds, such as fatty acids, fatty alcohols, phytosterols and triterpenes. The chromatographic separation of the compounds was achieved in a chromatographic run of 25.5 min. The best conditions for the dispersive liquid–liquid microextraction were 100 μL of CHCl₃ in 1 mL of acetone. For the injection-port derivatization, the best conditions were at 280 °C, 1 min purge-off, and a 1:1 sample:derivatization reagent ratio (v/v) using N-methyl-N-(trimethylsilyl)trifluoroacetamide (MSTFA):pyridine (1:1) as reagent. Quality parameters were assessed for the target compounds, giving a limits of detection (LODs) ranging from 1.1 to 5.7 ng/mL and limits of quantification (LOQs) from 3.4 to 18.7 ng/mL for linoleic and stearic acid, respectively. Repeatability (%RSD, n = 5) was below 11.51% in all cases. In addition, the method linearity presented an r² ≥0.990 for all ranges applied. Finally, the method was used to test the lipophilic fraction of various samples of commercial fruit juice.